FPRL-1 (N-formyl peptide receptor like-1) is a G protein-coupled receptor that is expressed on inflammatory cells such as monocytes and neutrophils, as well as T cells and has been shown to play a critical role in leukocyte trafficking during inflammation and human pathology. FPRL-1 is an exceptionally promiscuous receptor that responds to a large array of exogenous and endogenous ligands, including Serum amyloid A (SAA), chemokine variant sCKβ8-1, the neuroprotective peptide humanin, anti-inflammatory eicosanoid lipoxin A4 (LXA4) and glucocotricoid-modulated protein annexin A1. FPRL-1 transduces anti-inflammatory effects of LXA4 in many systems, but it also can mediate the pro-inflammatory signaling cascade of peptides such as SAA. The ability of the receptor to mediate two opposite effects is proposed to be a result of different receptor domains used by different agonists.
Activation of FPRL-1 by lipoxin A4 or its analogs and by Annexin I protein has been shown to result in anti-inflammatory activity by promoting active resolution of inflammation which involves inhibition of polymorphonuclear neutrophils (PMNs) and eosinophils migration and also stimulate monocyte migration enabling clearance of apoptotic cells from the site of inflammation in a nonphlogistic manner. In addition, FPRL1 has been shown to inhibit NK cytotoxicity and promote activation of T cells which further contributes to down regulation of tissue damaging inflammatory signals. FPRL-1/LXA4 interaction has been shown to be beneficial in experimental models of ischemia reperfusion, angiogenesis, dermal inflammation, chemotherapy-induced alopecia, ocular inflammation such as endotoxin-induced uveitis, corneal wound healing, re-epithelialization etc. FPRL-1 thus represents an important novel pro-resolutionary molecular target for the development of new therapeutic agents in diseases with excessive inflammatory responses.